Phosphoric acid

Claim 1

IN A METHOD FOR PREPARING AN IMPROVED, NON-FILTERABLE, FLUORIDE-CONTAINING WET PHOSPHORIC ACID CAPABLE OF BEING ADMIXED WITH OTHER PLANT NUTRIENTS TO PREPARE A COMPLETE LIQUID FERTILIZER, SAID PHOSPHORIC ACID BEING SUBSTANTIALLY FREE FROM ALUMINUM AND IRON ION PRECIPITATION WHEN NEUTRALIZED WITH AMONIA, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF: DIGESTING PHOSPHATE ROCK WITH SULFURIC ACID IN AN AQUEOUS ENVIRONMENT TO PREPARE A MIXTURE OF CALCIUM SULFATE AND CRUDE WET PHOSPHORIC ACID, THE LATTER CONTAINING ABOUT 30% TO 64% P$O$, 0.5%-54% FREE WATER, 0.4% TO 3.2% FLUORIDE ION CALCULATED AS FLUORINE, O.4% TO 2.5% IRON, CALCULATED AS FERROUS OXIDE, AND 0.4% TO 3.7% ALUMINUM, CALCULATED AS ALUMINUM OXIDE; FILTERING THE RESULTANT MIXTURE TO REMOVE THEREFROM CALCIUM SULFATE; CONCENTRATING THE THUSOBTAINED FILTRATE CONTAINING SAID IRON ALUMINUM AND FLUORIDE IMPURITIES BY HEATING THE SAME TO A TEMPERATURE BETWEEN ABOUT 50*C. AND 250*C. UNDER A REDUCED PRESSURE OF ABOUT 12.5 MM. TO ABOUT 250 MM., THEREBY ELIM INATING AT LEAST 95% OF THE FREE WATER; INTERMIITTENTLY REMOVING A PORTION OF THE SO-CONCENTRATED WET PHOSPHORIC ACID; SUBJECTING THE LATTER PORTION TO NEUTRALIZATION WITH AMMONIA; TERMINATING THE AFOREMENTIONED CONCENTRATION OPERATION OF THE REMAINING PORTION AT THE INSTANT WHEN IRON AND ALUMINUM IONS IN A REMOVED PORTION OF THE SOCONCENTRATED WET PHOSPHORIC ACID DO NOT PRECIPITATE IN THE FORM OF THEIR CORRESPONDING PHOSPATE SALTS THEREBY ESTABLISHING A P2O5 CONTENT IN SAID ACID RANGING BETWEEN 66% AND 72%; AND THEREAFTER RECOVERING A NON-FILTERABLE, FLUORIDE-CONTAINING, WET PHOSPHORIC ACID HAVING A P2O5 CONTENT RANGING BETWEEN ABOUT 66% TO 72%, ALL PERCENTAGES MENTIONED ABOVE BEING BY WEIGHT.